Stir the powdered milk into the milk in your crockpot. Adding powdered milk increases the protein content of the finished yogurt, and also gives it a thicker and creamier texture.

Turn the crockpot on Low, and heat the milk until it reaches 180°F (around 4-5 hours). Turn off the crockpot and allow the milk to cool slightly.

Once the milk has cooled to somewhere between 95-115°F, scoop a small amount of the milk out and add it to the 1/2 cup of plain yogurt with active cultures. Stir the yogurt and milk well until completely blended, then pour the yogurt mixture back into the rest of the milk.

Transfer the milk mixture into several jars or an enameled dutch oven, and place in your oven with the light on. Let the yogurt sit in the oven for 8 to 12 hours to complete the culturing process. DO NOT stir, jostle, or jiggle your yogurt during this time!

At the end of the culturing time, move the container(s) to the fridge and chill well before eating.